1. Field of the Invention
The present invention relates to an organic photoelectric conversion device having an organic photoelectric conversion layer that performs photoelectric conversion of incident light and generates signal charges.
2. Description of Related Art
Each of single-plate image sensors currently in use, notably CCD image sensors and CMOS image sensors, has three or four kinds of color filters in mosaic pattern on an array of pixels capable of performing photoelectric conversion (photodiodes), and produces outputs of color signals corresponding to its respective color filters. The outputs of color signals produced are formed into color images by undergoing signal processing. However, when color filters installed in mosaic pattern in an imaging device are filters of primary colors, about two-thirds of incident light is absorbed by color filters, accordingly there is a drawback that light utilization is inefficient and sensitivity is low. In addition, since color signals of only one color are obtained from each of pixels, resolution is low. In particular, false colors are noticeable.
In order to overcome those drawbacks, the imaging device as disclosed, e.g., in JP-T-2002-513145 has so far been developed. In the case of such an imaging device, triply stacked wells provided for light signal detection (photodiodes) in a silicon substrate deliver signals having different spectral sensitivities in response to their respective depths in the silicon substrate (signals having their individual peaks in the blue, green and red wavelength regions in the order of increasing distance from the surface). Although that device shows improvements in resolution and utilization efficiency of light, it has also drawbacks that color reproducibility is poor because of insufficiency in separation of spectral sensitivity characteristics of RGB output signals and S/N is degraded by addition and subtraction of output signals performed for obtaining true RGB signals. Therefore, as disclosed in JP-T-2002-502120 and JP-A-2002-083946, the imaging devices capable of achieving further improved separation of spectral sensitivity characteristics of RGB output signals have been researched and developed. Such imaging devices are imaging devices of three-photoelectric conversion layer structure, such as pixel structure made up of stacked photoelectric conversion layers generating signal charges in response to B light, G light and R light, respectively, in increasing order of distance from the incident plane of light and besides, each of them is provided integrally with a readout section which, on a pixel basis, can independently read signal charge optically generated in each photoelectric conversion layer. Therefore, in the case of such image pickup devices, incident light is subjected to photoelectric conversion and read, so utilization efficiency of visible light is close to 100%, and what's more, every pixel can deliver color signals of three colors R, G and B. Further, spectral sensitivity characteristics of three-layer photoelectric conversion layers can be chosen in isolation from one another, so separation of spectral sensitivity characteristics of ROB output signals is good. Thus, images of good color reproducibility and high S/N can be obtained in high sensitivity and high resolution (in inconspicuous false colors).
In the solid-state image pickup devices using organic photoelectric conversion layers disclosed in JP-T-2002-502120 and JP-A-2002-083946, pixel electrodes are built in a state that each pixel is partitioned, and thereon an organic photoelectric conversion layer and a counter electrode are stacked and shared by all pixels. Herein, field intensity is smaller on the gap between adjacent pixel electrodes than on each pixel electrode, so there is a problem that it takes time before signal charges generated in the gap come to be read, accordingly image lags occur.